The bells found in the tomb of the Marquis Yi are now in the collections of the China's Hubei Provincial Museum. (Wikimedia Commons/Vmenkov)

Copper was the most valuable metal for a thousand years.

As our technology advances different metals become more valuable. Silver for example was more valuable when we used it for photography. Platinum demand soared with catalytic convertors, and now lithium is in great demand thanks to the new batteries.

The metal that was most highly desired for the longest time is copper. This is because copper is needed to make bronze, the metal used for making the best weapons during the Bronze age. In China this period started around 1,700 BC and ended 1,000 years later with the adoption of steel weapons around 700 BC.

Many people heard of the early Chinese strongman who listened every morning to a tune that involved the ringing of each one of his large collection of bronze bells.

The common understanding was that he enjoyed the music. This was probably true, but there was a more practical and less known fact.

After winning a war, the prevailing leader will keep his own guard well armed and will order all other weapons melted and made into bells. Listening to a familiar tune was a quick way to take inventory and, if a note was missing, then know that trouble was brewing and to prepare accordingly.